Metal culverts have been used in building roads for a long time because metal pipe is lighter than concrete pipe and road crews needed special equipment to set heavier concrete pipes in road cuts. Metal pipes started as galvanized plates, which were bolted or riveted together. They later became rolled pipes which were fabricated at a plant and then installed in twenty-foot lengths to be jointed with a band to other twenty-foot segments to form a long culvert.
Metal pipe inverts will experience failure over time, which has been blamed on rust or corrosive soil conditions. Further analysis indicates that the failure is caused by continuous movement of sediment through the drain via drain water, effectively “sand blasting” or eroding the bottom of the pipe. Once protective elements have eroded portions of the pipe, then the pipe will rust.
Removing the metal pipes having failed inverts is an extraordinarily expensive and time consuming job. In particular, the soil must be removed to expose the pipe experiencing failure. The excavated hole must be wide enough to prevent further soil collapse. The bed must then be reworked, such as with crushed stone. The bed must be on an even stable grade to prevent pipe separation at the joints, and the replaced material must be compacted. Once that step is complete, base and pavement layers must then be replaced.